1. Field of the Invention
The present invention relates to a magnetic brush developing device for developing an electrostatic charge image and used for an electrophotographic apparatus such as copying machine, printing machine and the like, and more particularly to a toner supplementing device for supplementing toners to a developing agent contained in a housing of a magnetic brush developing device.
2. Description of the Prior Art
In the magnetic brush developing device, use is generally made of a two component developing agent consisting of carriers made of magnetic material and toners made of thermoplastic resin of low melting point and mixed with dye or pigment such as carbon black. Such a two component developing agent is stirred and mixed in the developing device and the toners are charged due to friction between the toners and carriers to a polarity opposite to that of an electrostatic charge image on a charge retentive member such as a photosensitive drum.
In such a developing device, since the toners are consumed each time the developing operation is effected, the developing device is provided with a hopper for containing toners and a device for supplementing a given amount of toners from the hopper so as to keep always a toner concentration of the developing agent to a desired value.
Various kinds of toner supplementing devices have heretofore been proposed. In one conventional toner supplementing device, provision is made of a hopper containing toners to be supplemented to a housing of a developing device and provided at its lower opening with a toner supplying roller having a longitudinal recess for receiving a given amount of toners from the hopper, the roller rotating intermittently in response to consumption of toners contained in the housing of the developing device so as to drop off the toners in the longitudinal recess into the housing and supplement the toners. However, such conventional device could not supplement toners in a stable state, since toners have not always a good fludity. As a result, the longitudinal recess of the toner supplying roller is stuffed with toner particles or the toner particles tend to bridge the surface of the roller. In order to avoid such defects, in another conventional toner supplementing device, the above mentioned hopper is provided at its lower opening with a resilient plate having one end operative to engage with the toner supplying roller and vibrate in response to the rotation of the roller so as to make toners flow down therethrough. In such a device, toners fall down through a slit-like space formed between side edges of the resilient plate and inner side walls of the housing of the developing device. This results in not uniform distribution of toners along the entire width of an electrostatic charge image to be formed on a charge retentive member and may cause a photographic fog at a peripheral portion of a picture.
In order to eliminate the above mentioned drawbacks of the conventional devices, an improved toner supplementing device which can obtain a picture having a better quality has heretofore been sought for.